Control apparatus for double-acting hydraulic cylinder and piston assembly

ABSTRACT

A safety vent valve or poppet valve assembly for a double-acting hydraulic cylinder, having duplex, opposed coaxial valve poppets closing a valve bore through the piston, and having a means to open the valve bore when the piston has moved beyond its working limits to provide a channel to vent fluid under predetermined excessive pressure. The venting of fluid under pressure when the piston has moved beyond its normal working stroke substantially reduces the force exerted by the piston upon the restraining machine member.

United States Patent Mercer [151 3,656,406 [451 Apr. 18, 1972 CONTROLAPPARATUS FOR DOUBLE- ACTING HYDRAULIC CYLINDER AND PISTON ASSEMBLYInventor:

Assignee:

pany, Cleveland, Ohio Filed: Feb. 1, 1971 Appl. No.: 111,328

U.S. Cl Int. Cl

Field of Search References Cited UNITED STATES PATENTS James R. Mercer,Akron, Ohio McDowell-Wellman Engineering Com- Kerr ........ .91/401...Fl5b 15/22 ..91/4o1 2,630,830 3/1953 Meddock .....91/40l 2,783,7443/1957 Tennis ....9l/40l 2,948,263 8/1960 Roger ....91/40l 3,004,52410/1961 McCoy et a1. ..91/401 Primary Examiner-Paul E.MaslouskyAttorney-McNenny, Farrington, Peame & Gordon [57] ABSTRACT A safety ventvalve or poppet valve assembly for a double-acting hydraulic cylinder,having duplex, opposed coaxial valve puppets closing a valve borethrough the piston, and having a means to open the valve bore when thepiston has moved beyond its working limits to provide a channel to ventfluid under predetermined excessive pressure. The venting of fluid underpressure when the piston has moved beyond its normal working strokesubstantially reduces the force exerted by the piston upon therestraining machine member.

7 Claims, 3 Drawing Figures PATENTEU APR 18 m2 SHEET 10F 2 INVENTORJAMES R. MERCER ATTORNEYS PATENTEDAPR 18 m2 3, 656.406

SHEET 2 0F 2 I46 I47 I35 F co INVENTOR JAMES E. MERCER CONTROL APPARATUSFOR DOUBLE-ACTING HYDRAULIC CYLINDER AND PISTON ASSEMBLY BACKGROUND OFTHE INVENTION AND PRIOR ART This invention relates generally to ahydraulic pistoncylinder assembly useful, for example, in mold-closingapparatus for an injection molding machine.

A hydraulic piston-cylinder assembly consists of a cylinder member and areciprocable piston member. In a mold-closing and clamping apparatus,such an assembly may be located between two end plates and supported bytie bars connecting the two end plates and arranged to move therealong.

An example of a prior art device of the type to which the presentinvention is particularly relevant and which provides a suitableenvironment for the present invention is shown in U.S. Pat. No.2,718,662. Also there is shown in U.S. Pat. Nos. 3,156,014 and 3,194,868another structure to which the teachings of the present invention may beapplied with advantage. The teachings of these patents are incorporatedherein by reference thereto.

With respect to U.S. Pat. No. 3,156,014, the patentee shows a movableassembly in which the force to expel hydraulic fluid from the cylinderis derived through a mechanical linkage from the power source used tomove the assembly along the tie rods. There is no provision in theassembly to mechanically restrain movement of the piston out of thecylinder beyond its normal stroke. Inadvertent introduction of hydraulicfluid into the cylinder chamber, when any other member ofthe machine isout of proper position to restrain the piston travel, for example, thethrust plate 72 (FIG. 5), or the locking members 29 (FIGS. 1- 3) of U.S.Pat. No. 3,156,014, will cause the piston to continue to move out of thecylinder. Considerable damage to related mechanical structures mayresult, necessitating the shut-down of the molding machine for extensiverepairs.

With respect to the device illustrated in U.S. Pat. No. 3,194,868, thecylinder-piston assembly has been altered to provide a plurality ofcompression springs to supply the force needed to expel the hydraulicfluid from the cylinder. There is also provided a plurality of safetyscrews to restrain movement of the piston out of the cylinder beyond itsnormal working stroke in the event of inadvertent introduction ofhydraulic fluid into the cylinder chamber while there is no externalmeans to restrain the movement of the piston out of the cylinder. Thepower means to move the piston-cylinder assembly is connected to itsadjacent member. The force to move the second member is transmittedthrough the plurality of compression springs. These springs willcompress, permitting the piston to be drawn from the cylinder chamber tothe limit of the safety screws, should the force needed to separate andopen the parts of the mold exceed the precompression of the springs.Once the mold has been opened, the springs will pull the cylinder memberover the piston portion of the piston member with sufficient force tocause a severe shock when the two members close one upon the other.

SUMMARY OF THE INVENTION The present invention is utilized mosteffectively in an improved mold-clamping piston-cylinder assemblylocated between two end plates as in the devices mentioned and with oneor both members of the assembly supported by the strain or tie rodsconnecting the two end plates for movement therealong. The piston memberand cylinder member of the assembly have been altered to form adouble-acting device which provides two opposed chambers, one on eitherend of the piston. The piston extension passing out through an aperturedend of the cylinder member can be made to extend or retract byalternately introducing hydraulic fluid to one cylinder chamber whilehydraulic fluid is vented from the cylinder chamber at the opposite endof the piston, such as by the use of a conventional hydraulic fluidfour-way directional control valve.

According to this invention, there is provided one or more valve boresthrough the piston connecting the two cylinder chambers, one at eitherend of the piston. Each such bore is normally closed by two opposedcoaxial valve poppets. The first and second valve poppets are arrangedto open as the piston extension moves out of the cylinder member beyondits predetermined normal working stroke. Thus,-the high pressurechamber, into which hydraulic fluid is being introduced through thefour-way valve, is vented through a channel formed by the valve bores orpassages and the open poppets and communicating with a low pressurechamber adjacent the opposite face of the piston which is in turn ventedthrough the same four-way direction valve. One poppet valve is openedmechanically and the other in response to fluid pressure of sufficientmagnitude to overcome biasing means, e.g. a spring.

The hydraulic fluid pressure in the high pressure chamber is thusgreatly reduced, thereby reducing the piston force proportionately atthe time the piston is restrained from further extension by the axiallimit of the vented low pressure chamber. Thus the cylinder structuremay be of substantially smaller proportions, comprising less materialand requiring less space than would be the case if the valve bore orbores and valve poppets were omitted from the piston.

Therefore, compared to prior art devices, the injection molding machineof the present invention is not subject to BRIEF DESCRIPTION OF THEDRAWINGS In the annexed drawings:

FIG. 1 is a fragmentary partial cross-sectional view of a part of aninjection molding machine and showing a pair of fixed end platessupported by tie rods or strain rods and a movable intermediate platecarried thereby, together with a pedestal assembly for preventingretrograde movement of the movable plate, as for example during molding.

FIG. 2 is a fragmentary cross-sectional view on an enlarged scaleshowing some details of a double-acting hydraulic fluid cylinder carriedby the intermediate plate shown in FIG. 1 and showing the poppet valveassembly in its nonnally closed position.

FIG. 3 is a fragmentary cross-sectional view of details similar to thoseshown in FIG. 2 with the piston displaced to its limit and the poppetvalve assembly open to by-pass fluid from the high pressure chamber tothe low pressure chamber.

DETAILED DESCRIPTION OF THE DRAWINGS While the poppet valve assembly ofthis invention is useful with any hydraulic ram system, it will beillustrated in conjunction with a closure means for an injection moldingmachine or a die-casting machine. As a suitable environment, then, thereis shown in FIG. 1 a portion of an injection molding machine forinjecting a therrnosetting material such as rubber. There is provided afirst end plate or base 10 and a second end plate 12, the end plates 10and 12 being held in spaced relation by cylindrical tie bars l4, l8 and20. As shown in FIG. 1, the ends of the strain rods are convenientlythreaded as, for example, with threads 22 on strain rod 14. The threaddiameter is less than the diameter of the strain rod so there isprovided a shoulder, such as shoulder 24, on strain rod 18. The endplates 10 and 12 may be tightly abutted against the shoulders such asshoulder 24, and held into position by strain rod nuts 26, 28, 30 and32, for example. Each end plate is provided with such nuts, thoseholding end plate 10 in position desirably being recessed, as shown, toreduce the overall length of the structure.

The end plate 12 is conveniently provided with an aperture 38 adapted toreceive a nozzle portion of an injection cylinder, one structure ofwhich is shown in U.S. Pat. No. 3,194,868. On its inner face 40, thereare provided mold-support means generally indicated at 42 adapted tohold a mold portion or section, e.g. one-half of a split mold. Themounting of this mold portion supporting structure is novel and obviatesthe use of cam-type clamps conventionally utilized for securing theupper mold support 42 in abutting relation with end plate 12. To thisend, there are provided hydraulic cylinders 44 and 46, each partiallyshown, secured to the remote surface of the end plate 12 and havingpiston rods such as a piston rod 45 extending in an axial directionthrough the end plate 12 from the remote surface to and beyond thesurface against which the mold portion 42 is normally in abuttingrelation. In vertical machines of considerable height, utilization of acam-type clamp of conventional design imposes difficulties in terms ofmanual access. Utilization of the hydraulically actuated extensible arms44 and 46 eliminates these clamping means, allows for movement of theupper mold-supporting plate structure 42 longitudinally of the machinefor more convenient access, and makes possible control of both theclamping operation and the longitudinal disposition thereof from acontrol panel located within easy reach of an operator.

Mounted for movement along the strain rods, e.g. strain rods 14 and 18,is a movable plate 48 fitted with suitable bushings such as bushings 50and 52. Laterally extending lugs 54 and 56 attached to plate 48 are alsoattached to double-acting hydraulic piston-cylinder assemblies 58 and60, whereby movement of the intermediate plate 48 along the strain rods14 and 18 is effected. In the embodiment shown in FIG. 1, the lugs 54and 56 are attached to rod members such as member 62. The rod membersare attached to a movable piston within cylinders 64 and 66, respectiely, in a known manner. The piston-cylinder assemblies 58 and 60 are inturn secured at their upper extremities to brackets 68 and 70 which arein turn secured to suitable mounting plates 72 and 74 bolted by bolts 76to the end plate 12. Operation of the piston-cylinder assemblies 58 and60 in unison causes movement of the movable plate 48 along strain rods14 and 18 in a conventional manner.

The upper face 78 of intermediate plate 48 is, in a manner similar tothe end plate 12, fitted with mold-support means generally indicated at80 of conventional design for supporting a mating mold portion orsection, not shown.

A piston-cylinder mold-closing assembly of a type useful in conjunctionwith the present invention is generally indicated at 84 mounted on theopposite face 82 of movable plate 48 from the mold-support means 80. Inthe embodiment shown, a piston-cylinder assembly 84 includes a cylindermember 86 and a piston member 88 in which piston 88 is movable relativeto the intermediate plate 48, and the cylinder portion 86 is secured tothe face 78 of intermediate plate 48 as by bolts 90. The piston member88 is also provided with a poppet valve assembly generally indicated at89, shown in enlarged detail in FIGS. 2 and 3, which permits fluidcommunication between a high pressure variable volume chamber 92 and alow pressure variable volume chamber 87. The chamber 92 defined by theconfronting faces 94 and 96 of movable plate 48 and movable piston 88,respectively, is adapted for receiving fluid under relatively highpressure as for example through port 98. Piston face 96 is referred tofor convenience as a high pressure face and the chamber 92 as a highpressure" chamber. When abutment means are provided for the externallyexposed surface 100 of the piston 88 extending through an opening 102 inthe end of cylinder 86, and the cavity or chamber 92 is filled withfluid, e.g. hydraulic oil, under pressure, retrograde movement of themovable head 48 is prevented and an extremely high closing force may bebrought to bear upon the mating mold portions (not shown) clampedbetween the mold support means 42 and 80, respectively. The relativelylarge diameter of the piston body 88 and the short stroke, e.g. about0.25 of an inch, relative to the diameters of the small diameter andlonger strokes of high-speed cylinders 58 and 60, enables closing of themold and the application of extremely high closing force without movinga great deal of liquid. Similar closure means are described in U.S. Pat.No. 2,718,662 in which a high pressure chamber such as chamber 92 ispressurized in a like manner during the molding operatron.

After the molding operation, the line communicating with the port 98(not shown) is vented to the oil reservoir to release the pressurizedfluid from high pressure chamber 92, and fluid under pressure isadmitted to chamber 87 through inlet port to lift piston 88 so as to befree from the pedestal 104. Chamber 87 is referred to herein forconvenience as a "low pressure chamber and the working face 135 ofpiston 88 as a low pressure face. The terms high and low" are relativeone to the other and refer to the conditions during molding, it beingunderstood that there are times in a cycle when the fluid pressure inlow pressure" chamber 87 is higher than the fluid pressure in the highpressure" chamber 92.

The abutment means comprises a pedestal generally indicated at 104. Thepedestal assembly in the illustrated embodiment includes an upstandingcylindrical post 106 mounted on a base 108. The entire pedestal assembly104 is laterally movable along guideway 110. In the position shown inFIG. 1, the pedestal is located for coaction with piston 88 to preventretrograde movement of the movable plate 48 along strain rods 14, 18 and20.

Guideway 110 is secured to end plate 10 by any suitable means such as bybolts 112. In order to move the pedestal assembly 104 out of retrogrademovement-preventing position, there is provided a device for convertingrotary movement to linear movement and including a fluid-actuated arm114 having mounted at its distal extremity a roller 116 which is mountedon an axis for rotating normal to the longitudinal axis of arm 114. Theroller 116 coacts with slot 118 milled into one side of the post 106. Fluid-operated motor means generally indicated at 120 coact in a suitablefashion with a shaft 122 which is dowelled or pinned (not shown) to thearm 114 at its proximal extremity. Rotation of the arm 114 clockwisethrough 180 will cause, therefore, a lateral displacement of thepedestal assembly 104 to the right-hand extremity of guideway 110.

In order to accommodate the outermost extension of the guideway 110,there is provided a platform 111 in coplanar relation with the uppersurface of end plate 10. The platform 111 is supported by the bracket113 (FIG. 1).

The uppermost portion of the post 106 is provided with extension meansin the form of a plurality of discs 132, any desired number of which maybe suitably mounted on the distal extremity of post 106 to adjust theoperative length thereof to accommodate differences in thicknesses ofthe combined mold portions. Any suitable means for securing the discs132 may be provided.

The poppet valve assembly indicated at 89 shown in enlarged detail inFIGS. 2 and 3 may be used singularly or in plural disposition in thepiston 88. Located in a generally cylindrical valve bore 131 through thepiston head 88 outside the peripheral boundary of the extension 100 ofthe piston 88 is a system of oppositely acting poppets 133 and 138 heldagainst seats 136 and provided in the valve bore 131 to close the valvebore during normal functioning of the double-acting hydraulicpiston-cylinder assembly 84. The valve stem 132 has an enlarged poppetvalve head 133 at the proximal end and a reduced diameter stem extendingto its distal extremity which is threaded to receive an adjustablecollar or nut 146 suitably locked thereto, as by a set screw. Interposedbetween the enlarged poppet valve head 133 and the nut 146, andconcentrically slidably fitted about the valve stem 132, are thesecondary poppet 138 fitted with a skirt portion 139 and the biasingspring as shown in FIG. 2. Sealing means 144 may be disposed in theportion of the secondary poppet 138 that is closely fitted to the stem132. The force of spring 145 tends to drive the opposed poppet valvefaces 134 and 140 of the poppet valve 133 and the secondary poppet 138,respectively,

against the opposed valve seat faces 136 and 142 provided in the passage131. The nut 146 of the poppet valve stem 132 extends beyond the lowerworking face 135 of thepiston 88 which forms the upper boundary of thelow pressure chamber 87 a distance adjustable to the desireddisplacement of the poppet valve 133 to mechanically lift its face 134from the seat 136 in the valve open position. The longitudinal distancebetween the lower end of the secondary poppet 138 and the adjacent faceof the nut 146 is set manually to approximately twice the distance thevalve stem 132 and the nut 146 extend beyond the face 135 of the piston88 as shown in FIG. 2.

The venting position of the poppet valve assembly is best illustrated inFIG. 3 where piston 88 of the piston-cylinder assembly 84 has moved toits fully extended position within the cylinder 86, its lower workingface 135 abutting the internal apertured end face 137 of the cylinder86. With the piston 88 in this extended position the distal end of thevalve stem 132 is also abutting the internal end face 137 of thecylinder 86. The abutment causes the poppet valve 133 to be lifted fromits seat 136 in the piston 88, thereby opening the hydraulic fluidchamber 92 into direct communication with valve bore 131. This exposesthe poppet valve surface 140 of the secondary poppet 138 to thehydraulic pressure existing in chamber 92. If the force of the hydraulicfluid pressure in chamber 92 impressed upon the exposed portion ofsurface 140 of the secondary poppet 138 should exceed the force or biasof the spring 145, the secondary poppet 138 will slide along the valvestem 132 toward abutment with the adjacent surface of the nut 146 toprovide direct communication between the valve bore 131 and hydraulicfluid chamber 87. This effectively vents high pressure fluid in chamber92 through valve bore 131 and chamber 87 to port 85 which is ventedautomatically by a four-way directional control valve (not shown),typically and conventionally used with double-acting hydrauliccylinders. Instead of a low pressure chamber 87, there may be providedmerely a vent or conduit to a reservoir. The second poppet permitspressurizing of chamber 87 to return the piston 88 to the zero strokeposition without by-passing hydraulic fluid through the valve bore 131into the high pressure chamber 92.

OPERATION OF THE MACHINE The operation of the embodiment of theinjection molding machine partially shown in FIG. 1 is essentially themode of operation as described in the aforesaid U.S. Pat. No. 2,71 8,662with useful improvements and refinements.

Briefly, injection means such as those shown in the aforesaid prior artpatents are mounted in the bore 38 provided in the fixed end plate 12.Any conventional injection means for moldable material including heatingelements may be used. A suitable cavity-type mold is secured to themoldsupport structures 42 and 80, the emplacement of the mating moldportions being accomplished with the pedestal assembly 104 in its fullyretracted position to the right of the guideway 110 as shown in FIG. 1.Extensible arms 58 and 60 are used to move movable plate 48 in adirection toward the fixed end plate to facilitate the placement of themold portions, not shown. When the mold is ready for injection,hydraulically actuated extensible arms 58 and 60 are used to move themovable plate 48 to the position shown in FIG. 1 at which point the moldis closed under the influence of the relatively small diameter pistonsin extensible arms 58 and 60. The pedestal assembly 104 is then moved bymeans of the arm 114 rotating in a counterclockwise direction as shownin FIG. 1 from the right-hand extremity of the guideway 110 to theposition shown in FIG. 1. Just prior to injection, fluid under pressureis introduced through port 98 into the chamber 92 between the piston 88and the lower face of movable plate 48, causing the piston 88 to movedownwardly and come into abutting relation with the post 106. Because ofthe large surface area of piston 88, extremely high closing force can bebrought to bear upon the mold whereby retrograde movement of the plate48 in response to the injection pressure is prevented. Programming meansgenerally indicated at 148 and including a slide bar 150 supported by' asuitable bracket means 152 secured to the end plate 12 cooperate with aslider 154 mounted on a bracket 156 which is in turn secured to themovable plate 48. The various sequences of operation are controlled bysuitably disposed and positioned switches carried by these programmingmeans, all in a well known and conventional manner. After injection andcuring, all in a known manner, the hydraulic fluid under pressure inchamber 92 is vented through port 98, and fluid under pressure isintroduced through port into chamber 87 on the end of piston 88 oppositechamber 92 to cause the piston 88 to move toward the lower surface 94 ofthe movable plate 48 and away from abutting relation with the post 106.The pedestal assembly 104 is retracted to its laterally removed positionby clockwise rotation of am 114, the mold opened by action of arms 58and 6t), and the casting removed from the mold.

If it should occur that the pedestal assembly 104 is in the retractedposition so as to be unable to prevent retrograde movement of thepiston-cylinder assembly 84 and pressurized fluid inadvertently admittedto the chamber 92, then the safety valve assembly 89 will function inthe manner stated above to prevent damage to the structure. Also, ifmold sections are not in place on the mold-supporting plates 42 and 80,the device will also function to prevent damage to the structure.

What is claimed is:

1. In a double-acting hydraulic cylinder and piston assembly including acylinder body having a high pressure end and an apertured end, a pistonbody reciprocable in said cylinder body between said ends in response tothe movement of pre surized hydraulic fluid and having a high pressureface in confronting relation to said high pressure end and defining ahigh pressure variable volume fluid receiving chamber therebetween, saidpiston having a low pressure face in confronting relation to saidapertured end and defining a relatively low pressure variable volumefluid receiving chamber therebetween, said piston having a pistonextension extending through said apertured end; and fluid inlet andoutlet means for each of said chambers, the improvement which comprisesa compound poppet valve assembly including:

a. a valve bore extending through said piston and having a pair ofopposed axially spaced valve seats therein, said bore communicating withsaid high pressure chamber and said low pressure chamber;

b. a valve stem concentrically disposed in said bore;

c. a first poppet valve member at the proximal extremity of said valvestem adapted for seating coaction with one of said valve seats;

d. means coacting between the distal extremity of the valve stem and oneend of said cylinder body for mechanically unseating said poppet valvemember in response to movement of said piston beyond a predeterminedpoint;

e. an oppositely acting second poppet valve concentrically and axiallyslidably mounted on said valve stem for coaction with the other of saidvalve seats; and

f. resilient means coacting between said valve stem and said oppositelyacting second poppet valve to bias the latter toward said first poppetvalve member and in opposition to pressurized fluid when said poppetvalve member is mechanically unseated.

2. A hydraulic'cylinder and piston assembly in accordance with claim 1in which the mechanical unseating means includes a collar secured to thedistal extremity of said valve stem.

3. A hydraulic cylinder and piston assembly in accordance with claim 2in which the collar is threadedly secured to said valve stem.

4. A hydraulic cylinder and piston assembly in accordance with claim 2in which the unseating means includes an abutment surface on theapertured end.

5. A hydraulic cylinder and piston assembly in accordance with claim 1in which the resilient means is a coil spring.

with claim 6 in which said second poppet valve includes a skirt portionsurrounding said coil spring and of an axial length for abuttingrelation with said collar when said second poppet valve is fully open.

1. In a double-acting hydraulic cylinder and piston assembly including acylinder body having a high pressure end and an apertured end, a pistonbody reciprocable in said cylinder body between said ends in response tothe movement of pressurized hydraulic fluid and having a high pressureface in confronting relation to said high pressure end and defining ahigh pressure variable volume Fluid receiving chamber therebetween, saidpiston having a low pressure face in confronting relation to saidapertured end and defining a relatively low pressure variable volumefluid receiving chamber therebetween, said piston having a pistonextension extending through said apertured end; and fluid inlet andoutlet means for each of said chambers, the improvement which comprisesa compound poppet valve assembly including: a. a valve bore extendingthrough said piston and having a pair of opposed axially spaced valveseats therein, said bore communicating with said high pressure chamberand said low pressure chamber; b. a valve stem concentrically disposedin said bore; c. a first poppet valve member at the proximal extremityof said valve stem adapted for seating coaction with one of said valveseats; d. means coacting between the distal extremity of the valve stemand one end of said cylinder body for mechanically unseating said poppetvalve member in response to movement of said piston beyond apredetermined point; e. an oppositely acting second poppet valveconcentrically and axially slidably mounted on said valve stem forcoaction with the other of said valve seats; and f. resilient meanscoacting between said valve stem and said oppositely acting secondpoppet valve to bias the latter toward said first poppet valve memberand in opposition to pressurized fluid when said poppet valve member ismechanically unseated.
 2. A hydraulic cylinder and piston assembly inaccordance with claim 1 in which the mechanical unseating means includesa collar secured to the distal extremity of said valve stem.
 3. Ahydraulic cylinder and piston assembly in accordance with claim 2 inwhich the collar is threadedly secured to said valve stem.
 4. Ahydraulic cylinder and piston assembly in accordance with claim 2 inwhich the unseating means includes an abutment surface on the aperturedend.
 5. A hydraulic cylinder and piston assembly in accordance withclaim 1 in which the resilient means is a coil spring.
 6. A hydrauliccylinder and piston assembly in accordance with claim 5 in which thecoil spring is biased between a collar secured to the distal extremityof said valve stem and said second poppet valve.
 7. A hydraulic cylinderand piston assembly in accordance with claim 6 in which said secondpoppet valve includes a skirt portion surrounding said coil spring andof an axial length for abutting relation with said collar when saidsecond poppet valve is fully open.